Liquid crystal displays (LCDs) have been widely used in graphic displays and TVs. Fast response, high transmittance, and wide view angle are the main requirements for high display quality that is critically required in large size monitors and TV applications. At present, the twisted nematic (TN) and super twisted nematic (STN) display devices are the main commercial products in the LCD market. Unfortunately, their inherent narrow view angle ability hinders them from going further. As one of the promising candidates, in-plane switching (IPS) mode liquid crystal display has been introduced for getting the high display quality in these areas.
The IPS concept was first published by R. A. Soref in Applied Physics Letters, vol. 22, p. 165 (1973) and the Journal of Applied Physics vol. 45, p. 5466 (1974). In 1992, Kiefer et al extended this operating principle to display devices and later Hitachi Japan developed it into commercial products. Referring to FIG. 1, in an IPS LCD 100, the electric field 105 is applied in the transverse direction and the LC molecules 110 in between the neighboring electrodes 115 are rotated in the same plane as the electrodes 115. Therefore, IPS mode LCD typically exhibits a wide view angle. From FIG. 1, the electric field 105 in the center of the electrodes 115 is zero so that the molecules do not rotate and result in a dark area between crossed polarizers 120, 125. The light efficiency of an IPS LCD is about 50-60% of the conventional TN LCD. The response time of a 4-μm IPS LC cell is approximately 25-30 ms.
To reduce response time and improve transmittance, S. H. Lee et al narrowed the distance between the neighboring electrodes 205, 215 to smaller than the width of the electrode and cell gap 210 as shown in FIG. 2. Under this condition, the electric field lines would be created in parabolic-like form and a fringe field effect would form in the whole substrate area. The IPS mode is transferred to the so-called fringe field switching (FFS) mode. Their results were published in Applied Physics Letters, vol. 73, p. 2881 (1995), and disclosed in U.S. Pat. No. 5,886,762 in 1999, U.S. Pat. No. 6,466,290 B2 in 2002 and U.S. Pat. No. 6,522,380 B2 in 2003.
In their electrode configuration, the rectangular shape or straight shape electrodes were used to produce the fringe field between the neighboring electrodes. This operation mode is defined as conventional FFS mode. The FFS mode needs a relatively high operating voltage (>6 Vrms) and, preferably, a negative dielectric anisotropy (Δε) liquid crystal material is used. The negative Δε LCs are more difficult to produce and have a higher viscosity.
Thus, there is a need for a new LCD structure that exhibits faster response time, higher transmittance, and wider view angle, where both positive (Δε>0) and negative dielectric (Δε<0) LC materials can be used.